1. Field of the Invention
The present invention relates to a needle assembly for collecting fluid, and more particularly, concerns a needle assembly for collecting a single sample of blood from a patient while providing an indication of entry of the needle assembly into the vein of the patient.
2. Description of the Prior Art
In the collection of body fluids, such as blood from a patient, the nurse or clinician collecting this fluid oftentimes must probe for or guess the location of the patient's vein. For instance, the nurse attempting to collect a blood sample, even with tourniquet pressure applied, cannot readily insert the needle in patients who have small veins or if the veins are not close to the skin surface. In those instances, the needle may either miss the vein entirely or perhaps may pass completely through a thin vein. As a result, blood flow through the needle into the evacuated blood collection tube would be uncomfortable and inefficiently slow since the blood would not be flowing from the patient's vein. The nurse would have to start over again and perhaps use another evacuated blood collection tube on the next attempt which, of course, would be wasteful of both materials and expense, not to mention the discomfiture which the patient experiences.
In order to reduce the waste of evacuated blood collection tubes which occurs in the blood collecting procedure where the nurse must guess at vein location, a number of blood collecting devices have been proposed which provide an indicator to the user that satisfactory vein entry has been accomplished. In these visual indicator devices, an antechamber is generally provided which is kept isolated by some sort of valving mechanism from the opening of the needle which deposits the blood being collected into the evacuated tube. Once the nurse probes for the vein and satisfactory entry is made, blood is supposed to flow through the needle into the antechamber to provide a telltale trace that the vein has been properly located. At this point in the blood collecting procedure, an evacuated blood collection tube is then usually inserted into the blood collection holder, opening up some type of valve whereby blood is then free to flow into the evacuated blood collection tube. Typical of these visual indicator blood collection devices are those found in U.S. Pat. Nos. 4,166,450 and 3,585,984.
Although in theory, this antechamber approach for the telltale trace of blood flow is workable, and oftentimes may work satisfactorily, there are, nevertheless, some inherent problems with this approach. For example, the antechamber generally is filled with air at the time the forward end of the needle is inserted into the vein of the patient. Inasmuch as the opposite end of the needle, for puncturing the evacuated blood collection tube, is valved or closed, the air in the antechamber forms a blockage since there is no place for such air to be displaced. Thus, even if the nurse locates the vein, and satisfactory entry is made with normal tourniquet pressure, the blood flow from the patient may not travel all the way through the needle before reaching the antechamber. This is due to the fact that the air in the antechamber blocks the blood flow through the needle even under normal tourniquet pressure. The net result of this is that the nurse will be deceived into believing that satisfactory vein entry has not been accomplished since no telltale trace will be visually observed. Unnecessary secondary venipuncture may take place which, again, is not only uncomfortable to the patient but is inefficient and wasteful.
Accordingly, improved approaches for providing a visual indicator to the user of a blood collecting device are still being sought. These improvements are needed in those types of blood collecting devices which make entry into the vein of the patient before the evacuated blood collection tube is inserted into the blood collection holder, which now is a very common blood collecting procedure.